International Patent Publication No. WO2009017009 discloses a technique, wherein voltages of the battery cells are equalized by charging or discharging battery cells having a voltage difference from the reference voltage (e.g., the smallest of the open-circuit voltages obtained from a plurality of battery cells constituting a battery pack) equal to or larger than a predetermined threshold value.
In addition, Japanese Patent Application Publication No. H09-015311A discloses a technique to estimate a reference voltage from a terminal voltage across a battery module constituting a battery pack (battery pack configured with battery cells), and to determine a failure of a battery cell in the battery module based on the reference voltage. Japanese Patent Application Publication No. H09-015311A describes that the reference voltage is obtained using an average value or a median of voltages of the battery cells in the battery module.
It should be noted that a SOC (State Of Charge) is generally obtained from an open-circuit voltage and the average value or the like is used, as described in Japanese Patent Application Publication No. H09-015311A, as the open-circuit voltage for obtaining the SOC.